A short polynucleotide with a free 3’ end, bound by complementary base pairing to the template strand and elongated with DNA nucleotides during DNA replication.Group of answer choicesRNA primertelomereOkazaki fragmentpromoterDNA primerNext

Many segments of these are joined together to make up the lagging strand of newly synthesized DNA.Group of answer choicesprimerOkazaki fragmenttelomereorigin of replicationNext

An enzyme that joins RNA nucleotides to make a primer during DNA replication, using the parental DNA strand as a template.Group of answer choicestelomerehelicaseclampSSBPprimasetopoisomeraseNext

Which reaction in DNA replication is catalysed by DNA ligase?Group of answer choicesBase pairing of the template to the newly synthesised strandFormation of a phosphodiester linkage between two Okazaki fragmentsProof reading the template strand for errorsAddition of nucleotides to the lagging strand

A short segment of DNA synthesized away from the replication fork during DNA replication.Group of answer choicesOkazaki fragmenttelomereprimerorigin of replicationpromoterNext

DNA polymerization is one of the most conserved mechanisms of genome replication.  Synthesis of a complete DNA strand requires a template, primers, a polymerase enzyme, and sufficient deoxyribonucleotide triphosphates (dNTPs).  The DNA polymerase enzyme binds consecutive base pairs on the template strand and extends the double helix by adding dNTPs to the primer.  The amino acid residues in the active site of DNA polymerase form hydrogen bonds with Watson-Crick donors and acceptors on incoming DNA nucleotides to facilitate base pairing.The formation of the DNA double helix creates opposing changes in entropy and enthalpy.  Favorable bonding interactions via hydrogen bonds during Watson-Crick base pairing results in negative enthalpy, and restricted rotation and flexibility of the DNA backbone generates negative entropy.  Scientists hypothesize that hydrogen bonding between bases not only stabilizes the double helix but is also crucial for selective and efficient replication.Analogs that are similar in size and shape to naturally occurring bases can be used to determine the influence of hydrogen bonding on base pair selectivity.  To mimic the structure of deoxythymidine triphosphate (dTTP), researchers synthesized dNTP derivatives of difluorotoluene (dFTP).  dFTP is a nonpolar analog of dTTP that lacks Watson-Crick hydrogen bonding.  Klenow fragment polymerase (KF), which has 3′-5′ but not 5′-3′ exonuclease activity, was incubated with a mixture of DNA template, primers, and dNTPs, including dFTP.  The efficiency of dFTP and natural dTTP nucleotide incorporation into a growing primer strand by KF is shown in Figure 1.Figure 1  Template-specific selection of dFTP and dTTP by the KF enzymeAdapted from Moran S, Ren RX, Kool ET. A thymidine triphosphate shape analog lacking Watson-Crick pairing ability is replicated with high sequence selectivity. Proc Natl Acad Sci USA. 1997;94(20):10506-11. Question 44The Klenow fragment used in the experiment would be able to perform which of the following repair processes?A.Correction of mismatched nucleotides in the middle of a completed strandB.Replacement of nucleotides at the 3′ end of the growing strandC.Excision of thymine dimers at the 5′ end of the growing strandD.Removal of damaged bases from the middle of the template strand